1. Field of the Invention
The present invention relates to electromechanical actuators, materials for electromechanical actuators, and methods of making electromechanical actuators.
2. Description of the Related Art
High-performance actuator materials capable of converting electrical energy into mechanical energy are needed for a wide range of applications including, but not limited to, mini- and micro-robots, micro air vehicles, flat-panel loudspeakers, micro-electromechanical systems (MEMS), and micro-fluidic devices. Actuator-material development goals include achieving a large range of motion with high precision and speed for meeting application requirements, high elastic energy density for robustness, and a low fatigue rate for durability and reliability. Although there are several actuator materials that are currently available, there are few, if any, that come close to meeting all of these goals.
Electroactive polymers (EAPs) attract much attention in the field of high-performance actuator materials because of their relatively low cost and ability to be tailored to particular applications. In particular, EAPs that are controlled by external electrical fields (generally referred to as field-type EAPs) have been demonstrated to exhibit relatively fast response speeds, low hysteresis, and high strain levels (e.g., greater than about 100%) that are far above those of traditional piezoelectric materials (e.g., piezoceramics). However, prior-art field-type EAPs also require relatively high electric fields, e.g., on the order of 100 V/μm, to generate usable elastic energy densities.
The elastic energy density is a key parameter, related to both the stress and strain generation capability of an actuator material. For example, for a material having linear dielectric and elastic properties, the stored elastic energy density, Us, can be expressed as follows:
                              U          s                =                                            1              2                        ⁢                          YS              2                                =                                                    (                                  K                  ⁢                                                                          ⁢                                      ɛ                    0                                    ⁢                                      E                    2                                                  )                            2                                      2              ⁢              Y                                                          (        1        )            where Y is the Young's modulus, S is the strain, K is the material's dielectric constant, E is the electric field, and ε0 is the vacuum dielectric permittivity (=8.85×10−12 F/m). Since, for most EAPs, the dielectric constant K is relatively small (typically less than about 10), relatively high electric fields are required for the generation of desirable elastic energy densities.